Discharge-lamp operating device using thyristor oscillating circuit

ABSTRACT

A circuit including a starting device and in which a discharge lamp is connected to the output terminal of a nonlinear thyristor oscillator. The thyristor oscillator includes a first closed circuit comprising a power source, a choke coil and a capacitor. This first closed circuit is set for a first oscillating condition. A second closed circuit is also employed. It comprises an inductance element and a voltage responsive switch such as a thyristor which elements are connected to said capacitor. This second closed circuit is set for a second oscillating condition, preferably near resonance state. A high frequency transformer can be combined with the second closed circuit in order to realize a faster turning on or initiation of the discharge lamp. In a hotcathode type discharge lamp, a third circuit for increasing preheating current is included in said oscillator circuit.

[54] DISCHARGE-LAMP OPERATING DEVICE USING THYRISTOR OSCILLATING CIRCUITInventors: Isao Kaneda; Kiyokazu Takeuchl, both of Otsu, Japan Assignee:

New Nippon Electric Company Ltd.,

Osaka, Japan Filed:

Feb. 26, 1970 Appl. No.: 14,325

Foreign Application Priority Data Feb. 27, 1969 Apr. 30, 1969 Apr. 26,1969 June 10, 1969 June 16, I969 US. Cl.

Japan ..44/15l06 Japan.. Japan..

Japan. Japan .44/47720 Int. Cl ..I-I05b 41/16, H0 5b 41/20, I-IOSb 41/23FieldofSearch ..3l5/99, 101, 105,241 R, 242,

315/244, DIG. 2, DIG. 7, 202, 207

[451 May 23, 1972 [56] References Cited UNITED STATES PATENTS 3,476,976I 1/1969 Morita et al. ..3 15/101 3,522,475 8/1970 Hashimoto ..3 1 5/239Primary Examiner-Herman Karl Saalbach Assistant Exarniner-'-MarvinNussbaum Attorney-Roberts & Cohen 57] ABSTRACT A circuit including astarting device and in which a discharge lamp is connected to the outputterminal of a nonlinear thyristor oscillator. The thyristor oscillatorincludes a first closed circuit comprising a power source, a choke coiland a capacitor. This first closed circuit is set for a firstoscillating condition. A second closed circuit is also employed. Itcomprises an inductance element and a voltage responsive switch such asa thyristor which elements are connected to said capacitor. This secondclosed circuit is set for a second oscillating condition, preferablynear resonance state. A high frequency transformer can be combined withthe second closed circuit in order to realize a faster turning on orinitiation of the discharge lamp. In a hot-cathode type discharge lamp,a third circuit for increasing preheating current is included in saidoscillator circuit.

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AI'TORNEYS DISCHARGE-LAMP OPERATING DEVICE USING TIIYRISTOR OSCILLATINGCIRCUIT BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates to discharge-lamp starting devices and moreparticularly to structurally simple devices for reliably startinglow-pressure discharge lamps, in which an oscillating high voltageproduced at the beginning of starting operation by the use of anon-linear thyristor oscillator is applied between the electrodes of thedischarge lamp. 1

2. Description of Prior Art According to the prior art, part of a chokecoil is utilized to generate a pulse voltage, and this pulse voltage issuperposed on the power source voltage to initiate the operation of adischarge lamp. In this arrangement, however, it is difficult togenerate the pulse voltage because magnetic saturation occurs in theassociated iron core when current is supplied to the main coil of thechoke for preheating the electrode. This requires the provision of anelectrode-heater transformer, and the over-all structure becomesinevitably complicated. Also, it is difficult to terminate generation ofthe pulse voltage after starting of the discharge lamp. As a result, thelife of the discharge lamp is curtailed and, as well, noise isintroduced into the power circuit.

On the other hand, voltage amplification is not obtained sufficiently bythe well-known pulse generator which uses a thyristor, so that apulse-transformer is required in the starting of discharge lamps. Suchstarting device has the disadvantage that pulse energy is decreased dueto the large winding ratio of the pulse-transformer used for voltagestep-up.

SUMMARY OF THE INVENTION It is an object of the invention to eliminatethe above-noted and other drawbacks inherent in the prior art and toprovide an improved discharge lamp operating device.

To achieve the above objects, there is provided in accordance with theinvention an improved discharge-lamp operating device having a firstcircuit device comprising a power source connected in series with adischarge lamp and a choke device for stabilizing the arc discharge ofthe lamp, and a second circuit device for starting the lamp connected inparallel thereto. The circuit device for starting the lamp comprises acapacitance element connected across the electrodes of the lamp and avoltage responsive switching element having an inductance elementconnected in parallel with said capacitance element.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1(A) to (B) are circuit diagramsand FIG. 1 (C) is a signal chart illustrating the principles ofoperation of a device embodying this invention;

FIGS. 2(A) to (D) are circuit diagrams and signal charts in accordancewith this invention;

FIGS. 3 and 4 are circuit diagrams showing other embodiment relating toFIGS. 2 (A) (D);

FIGS. 5(A) to 5(D) are a circuit diagram and signal charts showing otherembodiment of the invention relating to FIG.

FIG. 6 illustrates a modification of the embodiment of FIG.

FIG. 7 is a circuit diagram showing another modification of theembodiment of FIG. 1(A);

FIG. 8(A) illustrates a modification of the embodiment of FIG. 2(C) andFIG. 8(B) shows the waveform of the tube voltage of the discharge lampof FIG. 8( A);

FIGS. 9 through 1 I are circuit diagrams having an improved pre-heatingcircuit in accordance with further embodiments of this invention;

FIG. 12 is a circuit diagram suitable for operation at low temperature;

FIGS. 13(A) and (B) are circuit diagrams using a condenser for highfrequency heating and leading power-factor operations respectively;

FIG. 14 is another circuit diagram of a variation of FIG. 12;

FIGS. 15 through 20 are circuit diagrams of still further embodimentsfor the operation of a plurality of parallel discharge lamps; and

FIG. 21 is a circuit diagram showing an embodiment for the operation ofa plurality of series discharge lamps.

DETAILED DESCRIPTION The invention will hereinafter be explained indetail with reference to the appended drawings.

FIG. 1(A) illustrates an embodiment of the invention wherein an AC powersource 1, a choke coil 2 and a discharge lamp 3 having electrodes 4 and5 are connected in series. Also shown is a starting circuit 6 includinga condenser 7 and an inductor 8 thyristor 9 connected across thedischarge lamp 3 in parallel.

FIG. 1(B) is a modification wherein starting circuit 6' includes a highfrequency transformer 10 having a primary winding 11 and a secondarywinding 12. In this embodiment, a bidirectional element (for example, asilicon symmetrical switch) is used as the thyristor switching elementwhich turns on at a voltage below the'power source voltage and above thetube voltage of the discharge lamp. Instead of this element, aunidirectional element may be used.

The electrode preheating starting circuit is designed so that thiscircuit will have a high impedance with respect to the power sourcefrequency by virtue of the capacitor 7 when the thyristor switchingelement 9 is in its non-conducting state, or will have a low impedancewhen. the switching element 9 is in its conducting state, namely whenthe capacitor 7 is in its short-circuiting state.

The operation of this circuit will next be described below. When powerfrom the AC source 1 is supplied to the circuit, the capacitor 7 is notcharged at the beginning of each half cycle. In this state, theimpedance of this capacitor is zero. Accordingly, a small current flowsin a closed circuit including elements 1-2-4-7-5-1. As a result, theelectrodes 4 and 5 of the discharge lamp 3 are heated slightly andcharging of the capacitor 7 starts. When the voltage across thecapacitor 7 reaches a certain definite value at time t the thyristorswitching element 9 turns on and the capacitor 7 releases its chargerapidly into closed circuit including elements 7-8-9-7. Repeating theabove cycles, inductance voltage e across the terminals of the inductor8 is developed into a value nearly equal to that of condenser voltage e,across the condenser 7, and the condenser voltage e becomes higher thanthe breakover voltage V,,,, of the thyristor 9. As a result, anoscillating voltage is applied to the discharge lamp 3. When a currentpassing through the thyristor is decreased and cancelled by the currentflowing into the elements 1-2-4-8-9-5-1, it is impossible for thethyristor switching element 9 to sustain its holding current and theswitching element turns off.

In this way, a series of the above described operations occurs severaltimes whereby an oscillating voltage is generated out successive times.In the course of this operation, the instantaneous value of the currentis increased gradually. Thus, when the thyristor switching element 9turns on at time t and becomes able to sustain its holding current, theswitching element 9 maintains its conducting state whereby generation ofthe oscillating voltage is stopped at times as described hereinafter inFIG. 2(D), and the current for heating the electrodes 4 and Sisincreased to a normal value. Since the oscillation frequency issignificantly high, the second closed circuit is deemed to be ashort-circuit with respect to the source voltage having the frequency ofa commercial power source.

In the same way, a series of the above operations is repeated at eachhalf cycle and, as a result, the electrodes 4 and 5 are sufficientlyheated and thus the discharge lamp 3 is appropriately illuminated.suppresses When the discharge lamp 3 is once illuminated, thesemiconductor switching element cannot remain in the conducting statesince the conduction starting voltage of the switching element 9 ishigher than the tube voltage of the discharge lamp 3. Accordingly theoscillating voltage generator circuit automatically stops generating theoscillating voltage. Under this condition, the circuit 6 has a highimpedance against the power source frequency. This means that powerconsumption is decreased and the electrode 4 and of the discharge lamp 3are operated normally at all times.

In other words, this device is operated in such manner that thesemiconductor switching element S becomes conducting due to the voltageacross the capacitor C, the charge stored in the capacitor C beingrapidly discharged into the series circuit consisting of L and S, and aparallel resonance is brought about in the L-C circuit, therebyinitiating ignition of the discharge lamp. During the oscillation, thecurrent i, flowing in the capacitor C and also the current i, flowing inthe semiconductor switching element S take continuous oscillationwaveforms respectively as shown in FIG. 1(C). In FIG. 1(B), oscillatingvoltage induced in the primary winding 11 of the high-frequencytransformer is stepped up by the secondary winding 12 and is applied tothe lamp 3.

The embodiment of FIG. 2(C) is an improved circuit suitable particularlyfor a discharge lamp wherein emission is decreased (i.e. when the lifeof the lamp is terminating) or wherein the mercury vapor pressure islowered due to use of the lamp in a frigid environment, or wherein anelectrode filament is almost broken due to the condition in which thedischarge start voltage is extremely large due to a failure such asleakage in the discharge lamp. In such discharge lamp, it is inevitablethat a large current (such as more than 3 amperes in a watt lamp) iskept flowing. This serves to produce a considerable amount of heat inthe capacitor C due to dielectric loss. This means that the capacitorused for this device must be a high-frequency capacitor whose tamS issmall. Furthermore, the diameter of the winding of the high-frequencycoil L must be large enough to cope with this large current. Also anexpensive material producing little high-frequency loss must be used forthe magnetic core. In addition, the semiconductor switching element musthave a large current capacity.

FIG. 2(C) also shows an improvement with respect to discoloration of thedischarge lamp caused by applying the high-frequency voltage generatedby the starting circuit device, and with respect to short life of thelamp which is caused by keeping said high voltage impressed for a periodof about 100 cycles to initiate turn-on after the power switch has beenclosed.

Namely, the embodiment of FIG. 2(C) is characterized in that saidoscillation is stopped at an arbitrary phase angle before 1r/2 in eachhalf-cycle of the AC power supply. The principle of said oscillationstop at an arbitrary point will next be described relative to FIG. 2(A)in which two coils L and L are provided for a magnetic core T, alow-frequency power source EL is connected to the coil L by way of alow-frequency impedance ZL, and a high-frequency power source BI isconnected to the coil L via a high-frequency impedance ZI-I. In thiscircuit, it is assumed that the high-frequency voltage is kept constant,and the low-frequency voltage is used as a kind of bias Then, as shownin FIG. 2(B), since the magnetic core T has a hysteresis characteristic,the flux density B is largely varied by the low-frequency current 1during the period ab -c At 0, the magnetic core is saturated. The fluxdensity B is nearly constant for the period ad'. Hence, it becomespossible to oscillate the circuit only during the periods ac' and df' ofthe low-frequency current I whereby a high-frequency voltage is obtainedand the oscillation can be stopped during the periods ad' and f-a'.Similarly, an oscillation is produced during the periods a"-c" and d"fof a larger lowfrequency current I whereby high-frequency voltage isobtained, and the oscillation is stopped during the periods c-d" andf"a". (Strictly speaking, the B-I-I curve varies with a variation of thelow-frequency current; however, FIG. 2(B) shows only one B-I-I curve forsimplicity of explanation.)

In the above operation, it is arranged to vary the lowfrequency current.Instead, the high-frequency current may be varied. Also keeping thecurrent constant, a magnetic core having a different hysteresischaracteristic may be used.

FIG. 2(C) shows such an embodiment wherein an AC power supply 1 ofcommercial frequency, a choke coil 2, and a discharge lamp 3 havingelectrodes 4 and 5 are connected in series and wherein there is provideda starting device 6 including a capacitor 7 having a high impedanceagainst said commercial frequency, and a semiconductor switching element9 operatable according to the voltage across the capacitor 7. Thisdevice is different from the embodiment shown in FIG. 1 in that ahigh-frequency coil 14 is provided which has an intermediate tap viawhich power is supplied thereto.

The operation of the circuit of this embodiment will be explained below.When the AC power is supplied, the capacitor 7 is charged by way of part15 of the high-frequency coil 14 and the semiconductor switching element9 becomes conducting according to the voltage across the capacitor 7. Asa result the charge across the capacitor 7 is rapidly released via thecoil 14 whereby the capacitor 7 and coil 14 effect a resonance and ahigh-frequency voltage is thus obtained. In this operation, thedirection of current flowing in the part of coil 15 in the charging turnis the reverse of that in the discharging turn. Accordingly, themagnetic core of the high-frequency coil 14 is excited by thelow-frequency current which represents the difference between thesemutually reversed currents. Thus, when the core is saturated at anarbitrary phase angle before 1r/2 in each half-cycle of the AC powersupply, the flux density of the high-frequency coil 14 is no longervaried and the oscillation is stopped. As a result, the current i,flowing in the capacitor 7 becomes zero, the current i, flowing in thesemiconductor switching element 9 becomes a low-frequency current, andthis state is maintained to the end of the half-cycle. A series of suchoperations is repeated in each half-cycle of the AC power supplied andthus an intermittent oscillation voltage as shown in FIG. 2(D) isapplied to the discharge lamp 3. When the electrodes 4 and 5 aresufficiently heated, the discharge lamp 3 is illuminated. When thedischarge lamp 3 has been illuminated, the semiconductor switchingelement 9 cannot stay in its conducting state and the oscillation isstopped precisely as required. In this way, the discharge lamp 3receives no undesirable influence.

FIG. 3 shows another embodiment of the invention wherein a capacitor 17having a small capacity is connected in parallel with the high-frequencycoil 8. According to this circuit, the capacitor 17 connected inparallel with the inductor 8 varies the back-swing characteristic of theinductor 8 so as to make a smaller back-swing variation. Therefore,oscillation can be stopped at a small current i by using the capacitor17, at the time the voltage across the thyristor 9 reaches thebreak-over voltage V thereof. In this embodiment, it may be so arrangedthat a secondary coil is provided for the high-frequency coil 8, and thecapacitor 17 is connected to this secondary coil.

FIG. 4 shows another embodiment of the invention wherein a resistor 18having a high resistance is connected in parallel with the capacitor 7.According to this embodiment, the current flowing in the resistor 7serves to excite the high-frequency coil 8 in the direction against theflow of the discharge current. This circuit operates with the sameeffect as in the arrangements of FIGS. 2(C) and 3, which make itpossible to turn on the discharge lamp quickly and securely with the aidof oscillation on the initial drive. Furthermore, the oscillation periodcan be reduced to less than -n-/2 and, as a result, the oscillationcurrent can be set at an arbitrary value which is Vth to l/20th of thatrequired according to the embodiment of FIG. 1.

FIG. 5(A) shows a further embodiment which eliminates varying light atlow level at the beginning of a starting operation.

In FIG. 5(A), a starting device 6 includes a capacitor 7, asemiconductor switching element 9 and a high-frequency coil 19 having apair of windings 20 and 2 1. The capacitor 7 has a high impedance withrespect to power source frequency. The core of the high frequency coil19 consists of toroidal ferrite or the like, and is provided with a pairof windings 20 and 21 disposed in the oscillation circuit to be operateddemagnetizingly or in bucking relation.

The operation of the above circuit will next be explained. When power issupplied thereto from the AC power source 1, the capacitor 7 is charged.Due to this, the semi-conductor switching element 9 becomes conducting,and the capacitor 7 and high-frequency coil 19 oscillate. Thus, ahigh-frequency high voltage is applied to the discharge lamp 3. At thesame time, the electrodes 4 and 5 are heated by the current supplied tothe starting device 6. When the electrodes are sufficiently heated, thedischarge lamp is appropriately discharged for lighting and, afterstarting, the oscillation is automatically stopped in the manneraccording to the above-described embodiments of FIGS. 2 to 4. In thisembodiment, the starting operation is effectively carried out since thewindings 20 and 21 are connected demagnetizingly with each other.

More specifically, when the number of turns of the winding 21 is zero,the oscillation voltage will take a waveform as shown in FIG. 5(B). Whenthe winding 21 has its turn ratio 1 l with respect to the winding 20,the oscillation voltage will take the waveform shown in FIG. 5(C). Ifthe turn ratio between the two windings is 3 l, the waveform will be asshown in FIG. 5(D). In any case, the oscillation frequency becomes aboutten times that in FIG; 5(B). Furthermore, its instantaneous value isreduced and the envelope does not reach zero. Accordingly, the lightintensity is increased steadily during the beginning of the startingoperation. In other words, visibly comfortable starting can be realizedaccording to this arrangement.

The windings 20 and 21 are connected demagnetizingly with each otherand, hence, the combined inductance L of the ferrite core is varied withrespect to each instantaneous value. The value of di/dt is remarkablyincreased and the oscillation frequency is accordingly increased. At thesame time, the value of L (di/dt is decreased and the instantaneousvalue is accordingly decreased.

FIG. 6 shows a modification of this embodiment wherein the winding 21 isconnected in series with the oscillator circuit consisting of acapacitor 7 and a series circuit of the semiconductor switching element9 and winding 20. In this arrangement, the winding 21 through whichcurrent is supplied to the oscillator circuit is connecteddemagnetizingly to the winding 20 through which the discharge currentfrom the capacitor 7 flows whereby the same effect as shown in FIG. 5(A)is obtained. I FIG. 7 is another embodiment in which the supply ofhighfrequency voltage can be automatically stopped after starting of thelamp. This embodiment is characterized by the adding of a voltageresponsive switching element 22 connected in series with the oscillatingvoltage generator for starting discharge lamps as shown above. As shownin FIG. 7, a starting circuit including switching element 22 which iseffective in operation at low temperatures to eliminate defects due tothe elevated tube voltage is connected to a discharge lamp such as afluorescent lamp having a hot cathode. The same components as shown inFIG. 1 are indicated by the common references. The voltage generator 6is constituted of a capacitor 7, a voltage responsive switching element9 and a coil 8.

In this embodiment, when power is supplied to the circuit from the powersource 1, the power source voltage is applied to the element 22 by wayof the capacitor 7. Due to this, the element 22 becomes conducting, andthe capacitor 7 is charged. When the voltage across the capacitor 7reaches the operating voltage of the element 9, the element 9 becomesconducting, and the charge across the capacitor 7 is rapidly dischargedinto the closed circuit consisting of elements 7-9-8- 7. As a result, avoltage is induced in the coil 8 and is applied to the discharge lamp 3.Accordingly, the electrodes 4 and 5 are heated. A series of suchoperations is repeated at each half-cycle of the power source. When theelectrodes 4 and 5 are sufficiently heated, the discharge lamp 3 turnson. When the lamp 3 is illuminated, it becomes impossible for theelement 22 to stay in the conducting state any longer because theoperating voltage of the element 22 is higher than the tube voltage ofthe lamp 3. As a modification of FIG. 7, a circuit consisting of acondenser and a parallel resistor can be connected in parallel to theswitching element 22 in order to prevent radio noise.

When said resonance is utilized in the arrangement, a discharge lamp(e.g., a 40 watt fluorescent lamp) can be ignited reliably even at a lowtemperature such as 20 C. Thus, a high-frequency voltage is applied tothe circuit thereby initiating ignition of the discharge lamp and, oncethe lamp is illuminated, supply of the high-frequency or pulse voltageis terminated. In addition, the discharge lamp can be ignited at a verylow temperature.

FIG. 8(A) shows another embodiment which improves on the embodiment ofFIG. 2 and permits stable starting even at low temperature.

Generally, when a discharge lamp is initiated by AC power of commercialfrequency, the tube voltage takes a square waveform as shown in FIG.8(B). The leading edge of the wave is steep. This is because the arc isfirst extinguished and glow discharge is formed in the reverse directionand then another arc discharge is started. The width of this riseportion or leading edge is in the order of milliseconds. The widthincreases with an increase in the capacity of the noise preventingcapacitor usually connected in parallel with the lamp. In lowtemperature atmospheres, the rise is remarkably steep.

On the other hand, the break-over voltage V, of the semiconductorswitching element (e.g. thyristor) in the starting circuit 6 is lowerthan the maximum instantaneous value of the power source voltage andhigher than the maximum instantaneous value of the tube voltage of thedischarge lamp. This breakover voltage V has a sufficient amount ofmargin covering almost all kinds and capacities of fluorescent lampsunder normal operating conditions. However, when the discharge lamp isoperated in low temperature atmosphere or at a high tube voltage, orwhen the capacity of the capacitor 7 in the starting circuit 6 is large,said margin is not always sufficient, and the tube voltage will have avery high rise portion in its waveform as indicated by the dotted lineinFIG. 8(B). In some cases, the value of this rise portion AV is morethan 20 V. Hence, in some discharge lamps, the value AV exceeds thebreak-over voltage V,,,, of the semiconductor switching element 9. As aresult, it may often be the case that an oscillation is brought about atthe beginning of each half-cycle whereupon the lighting flickers or thearc discharge cannot be maintained.

The starting circuit 6 of this embodiment has an element such as adischarge tube 23 which allows current flow prior to turn-on of thethyristor 9 and which has a suitable impedance and is connectedsubstantially in parallel with the thyristor 9.

In the operating circuit arrangement shown in FIG. 8(A), the reference24 denotes a noise preventing capacitor. The capacitor 7 acts as a noisepreventing capacitor, if the part of coil 14 has a small impedance. Theignition voltage at which the discharge starts in the discharge tube 23is lower than the breakover voltage V of the semiconductor switchingelement 9.

The operation of this circuit will next be described. When power issupplied thereto from the AC power source 1, the capacitor 7 andhigh-frequency coil 14 of the starting circuit device 6 oscillate toturn on the discharge lamp. When the rise portion AV becomes large dueto, for example, a low temperature environment, the discharge tube 23releases its charge. Most of the energy due to V, is absorbed by thiscircuit. As a result, the thyristor becomes inoperative. Even if thethyristor 9 is operated, this will not bring about oscillation. Thus, astable discharge operation is maintained for the discharge lamp 3.

Instead of the discharge tube 23, a semiconductor switching element suchas a Diac which has a relatively large operating resistance may be used,or a resistor may be used. By such means, a stable discharge conditioncan be maintained even at a low temperature such as 5 to 10 C.

For increasing current to pre-heat the filament of a discharge lamp ofpre-heat type during the starting period,

various operating circuit arrangements are possible in accordance withthe invention.

FIG. 9 is an embodiment characterized by a current-increasing circuit'30for pre-heating the filament. This arrangement essentially comprises aclosed circuit of a condenser 31 and a diode 32 connected in series withthe condenser 31. The current-increasing circuit 30 is connected betweenthe electrode 4 and the starting circuit device 6 described in thefundamental embodiment of this invention shown in FIG. 1(A). In order toadjust the charge and discharge period of the condenser 31 and tocontrol the preheating current for the lamp 3, a resistor may beconnected to the condenser 31 in parallel or in series. It is alsopossible to use a thermistor as a resistance element as part of all ofthe resistance component.

FIG. is another embodiment. In this embodiment, increasing circuit 30comprises a coil section 33 of the choke coil 2 and a semiconductorswitching element 34 connected in parallel with the divided coil section33. When the first high oscillating voltage is produced by the startingcircuit device 6, the semiconductor switching element 34 is conductingdue to the effect of d V/dt, and the pre-heating current can thus beincreased.

FIG. 11 shows another embodiment of this invention. This arrangement, acurrent-increasing circuit 30" for pre-heating the filament of the lampcomprises a coil winding 5 connected demagnetizingly with the choke coil2. Circuit 30 is connected between the electrode 4 of the lamp 3 and thestarting circuit device 6, thereby eliminating the use of thesemiconductor switching element 34 in the embodiment of FIG. 10.

For improvement of the tube voltage as described in the embodiment ofFIG. 8(B), a diode 36 can be connected between the electrode 4 of thelamp and the starting circuit as shown in FIG. 12. The diode 36supresses the peak voltage caused by charging the condenser 7 onreversing the current.

FIG. 13(A) shows a further embodiment for a leading power factor, inwhich a condenser 37 is connected in series between the choke coil 2 andone filament of lamp 3. A resistor 38 is usually used to protect againstcapacitor failure.

FIG. 13(B) shows a still another embodiment for pre-heating the filamentby both high and low frequency. The circuit arrangement includes acondenser 39 in the first closed circuit, which is connected in parallelacross the lamp 3. The capacitor 39 can pass the current i in the secondclosed circuit through the filament because of the high frequency. Onthe other hand, the current i from the power source 1 flows through thefilaments of the lamp during the pre-heating period. Therefore, both thehigh and low frequency currents can heat the filaments of the lamp 3. Asa result, ignition of the lamp is achieved rapidly by increasingfilament currents.

FIG. 14 shows a further modification of FIG. 12 in which a thyristor 40having a break-over voltage higher than the starting voltage of the lampis connected in parallel with the lamp 3. An impedance means, which isoriginally used for reducing the current flowing into the thyristor 40and which also acts as a stabilizer against an abnormal oscillation, isconnected in series with the starting circuit device 6.

FIGS. 15 through 20 are circuit arrangements for a plurality of paralleldischarge lamps. FIG. 15 shows a circuit arrangement having a singlestarting circuit and a pair of lamps. This circuit is considered ascombination of embodiments in FIGS. 1(8) and 9. A condenser 42 forpower-factor improvement and a condenser 43 for preventing noise areconnected in parallel with the power source 1.

FIG. 16 illustrates a modification of the circuit arrangement of FIG. 15in which the choke coil is divided into two portions 44 and 45 and thepair of diodes 36 and 36' are connected between the capacitor 7 or 7'and the thyristor 9. In the circuit arrangement of FIG. 17, one of apair of condenser 46 and 46 for power-factor improvement can be used ina pre-heating circuit and semiconductor switching elements 47 and 47'are used in substitution for diodes 36 and 36 in FIG. 16. Furthermodifications are disclosed in FIGS. 18, 19 and 20, in which thereferences are the same as the hereinbefore described embodiments.

FIG. 21 shows a typical embodiment for the sequence circuit which isbased on the embodiment of FIG. 1(A).

What is claimed is:

1. Apparatus comprising a first closed circuit including a power supply,a choke and a discharge lamp connected in series in said closed circuit;and a second closed circuit including a semiconductor switching element,a capacitor and an inductance element separate from said choke, saidswitching element and inductance element being connected in series witheach other and in parallel with said lamp, said capacitor also being inparallel with said lamp, the lamp being adapted for being ignited and indischarging state having a characteristic tube voltage, said switchingelement being characterized by a conduction starting voltage which ishigher than said tube voltage, said capacitor and inductance elementforming a resonant circuit adapted for generating an oscillat ingvoltage which is applied to said lamp, said lamp including electrodesrespectively connected between said power supply and capacitor, saidpower supply charging said capacitor through said electrodes which arethereby heated, said switching element conducting when the capacitorachieves a charge equal to said conduction starting voltage whereuponsaid oscillating voltage is developed by said resonant circuit, theheating of said electrodes and the developing of said oscillatingvoltage igniting said discharge lamp, the tube voltage of which preventsthe switching element from conducting.

2. Apparatus as claimed in claim 1 comprising a further capacitorconnected across said inductance element.

3. Apparatus as claimed in claim 1 comprising a resistor connectedacross said capacitor.

4. Apparatus as claimed in claim 1 comprising a further capacitor forleading power factor connected in series with said choke and lamp.

5. Apparatus as claimed in claim 1 comprising a further capacitorconnected in parallel with said lamp at the side opposite to said secondclosed circuit.

1. Apparatus comprising a first closed circuit including a power supply,a choke and a discharge lamp connected in series in said closed circuit;anD a second closed circuit including a semiconductor switching element,a capacitor and an inductance element separate from said choke, saidswitching element and inductance element being connected in series witheach other and in parallel with said lamp, said capacitor also being inparallel with said lamp, the lamp being adapted for being ignited and indischarging state having a characteristic tube voltage, said switchingelement being characterized by a conduction starting voltage which ishigher than said tube voltage, said capacitor and inductance elementforming a resonant circuit adapted for generating an oscillating voltagewhich is applied to said lamp, said lamp including electrodesrespectively connected between said power supply and capacitor, saidpower supply charging said capacitor through said electrodes which arethereby heated, said switching element conducting when the capacitorachieves a charge equal to said conduction starting voltage whereuponsaid oscillating voltage is developed by said resonant circuit, theheating of said electrodes and the developing of said oscillatingvoltage igniting said discharge lamp, the tube voltage of which preventsthe switching element from conducting.
 2. Apparatus as claimed in claim1 comprising a further capacitor connected across said inductanceelement.
 3. Apparatus as claimed in claim 1 comprising a resistorconnected across said capacitor.
 4. Apparatus as claimed in claim 1comprising a further capacitor for leading power factor connected inseries with said choke and lamp.
 5. Apparatus as claimed in claim 1comprising a further capacitor connected in parallel with said lamp atthe side opposite to said second closed circuit.